Oracle 1z0-071 Exam With Confidence Using Practice Dumps

Unused columns are a feature in Oracle that allows a column to be marked as unused without immediately dropping it from the table structure. The key points for each option are:

A. The DESCRIBE command does not display unused columns. These columns are also not visible in user_tab_cols but are visible in user_unused_col_tabs.

B. Primary key columns can be set to unused, but you must drop the primary key constraint before doing so.

C. Once a column is marked as unused, it is not possible to query it, and Oracle will not allow DML operations on that column.

D. This is true. Once a column is set to unused, you can add a new column with the same name because Oracle essentially considers the unused column as removed from the table.

E. Just like primary key columns, a foreign key column can be marked as unused, but you must drop the foreign key constraint first.

F. This is true. Unused columns retain their data until the column is dropped using the DROP UNUSED COLUMNS command.

References:

Oracle Database SQL Language Reference, 12c Release 1 (12.1): "ALTER TABLE"

Oracle Database Administrator’s Guide, 12c Release 1 (12.1)

A: NEXTVAL is used to increment the sequence and return the next value; it does not give the last number generated.

B: CURRVAL returns the current value of the sequence, which is the last value generated in the user's current session. However, CURRVAL cannot be queried unless NEXTVAL has been called at least once in that session.

C: CURRVAL is used correctly, but the syntax 'sequence.CURRVAL' is not correct in Oracle SQL.

D: NEXTVAL is used to generate the next sequence number, not to retrieve the last one generated.

For the SELECT statement from two tables without a JOIN clause:

Option B: You can add a WHERE clause with filtering criteria.

A WHERE clause can be added to a query to filter the results based on specified conditions.

Option E: It returns the same rows as SELECT * FROM bricks CROSS JOIN colors.

A comma-separated list of tables in a FROM clause is equivalent to a CROSS JOIN, resulting in a Cartesian product of the tables.

Options A, C, and D are incorrect because:

Option A: You cannot add an ON clause without changing the comma-separated FROM clause to a proper JOIN.

Option C: It returns the Cartesian product, not the sum, of the rows from BRICKS and COLORS.

Option D: A USING clause is not applicable without changing the syntax to a proper JOIN.